This invention relates to control of adhesive bond strength where a silane coupling agent is used to promote adhesion, and is particularly applicable for bonding ceramic brackets to teeth for orthodontic braces.
A recent development in the field of orthodontic appliances provides transparent or translucent ceramic brackets for adhesive bonding to teeth. An arch wire is secured to such brackets in a conventional manner for making orthodontic adjustments. Such a ceramic bracket is particularly advantageous since it has outstanding mechanical strength and is cosmetically acceptable since the underlying tooth color shows through the bracket.
Such brackets may be made of single crystal or polycrystalline aluminum oxide for superior optical and mechanical properties. It can, however, be difficult to bond aluminum oxide adhesively to the surface of a tooth since adhesion between aluminum oxide and acceptable dental adhesives is relatively low. Therefore, a layer of high silica ceramic such as a layer of glass can be provided on the base of the bracket, that is, the surface to be bonded to the tooth. The silica containing surface is then "primed" or "silanated" with a conventional silane coupling agent. An exemplary silane coupling agent comprises gamma-methacryloxypropyl trimethoxysilane. Conventional acrylic and methacrylic resin dental adhesives bond strongly to such a silane-treated surface and form a secure bond to the face of the tooth.
It is desirable to provide a technique that provides adhesion with a strength that is subject to easy control. It is also desirable that such a technique be applicable to adhesive bonding of other substrates.